It is proposed to prepare a series of aminoacyl derivatives of nucleosides, chloramphenicol and an analog of C-A-Gly to investigate structural, conformational and stacking requirements of ribosomal peptidyl transferase. The preparation of a series of possible transition state analogs of the peptide bond formation step of protein synthesis is also proposed. The obtained products will be investigated in an E. coli cell-free system as substrate (acceptors) or inhibitors of ribosomal peptidyl transferase and in the leukemia L-1210 system as potential antitumor agents. The preparation of a series of purine diribonucleoside phosphates is devised to investigate the influence of electronic effects on base stacking and possible correlation with the acceptor activity of the corresponding series of 2'(3')-O-L-phenylalanyl purine ribonucleosides.